Known systems having flight bars mounted on chains for moving cartons along the working reach of the machine may be moved onto the return reach by passing their support chains over sprockets having small radii and which may cause an angular acceleration of the flight bars as they are rotated onto the return reach so that a carton being moved by such a flight bar must be accelerated at a faster speed away from the flight bar in order to prevent damage to the carton by the downwardly accelerating flight bar.